| Northeast sandy land is one of the most east-end and high-latitude sandy lands in china.With the global climate change,northeast sandy land has gradually become the mainstream hot spot.As an important part of the north china desert,the in-depth study of its material composition is of great significance to the study of Asian dusty system.the composition of heavy minerals and Sr-Nd isotopes contains important parent rock information and is an important tool to unravel the sediment evolution process and source tracer.systematic research is helpful to reveal the path and evolution process of dust migration during the geological period.At the same time,the"granularity effect"caused by sorting has always been the heavy mineral and constraints on the isotopic composition of Sr-Nd.to enrich the material composition and explore the effect of sorting on the composition of heavy minerals and Sr-Nd isotopes,19 aeolian sand and river sand samples were collected and treated with grain separation in huir sand.among them,12 sub-samples?<73?m and 73–125?m two grained levels?were identified and analyzed.23 sub-samples?<63?m,<30?m and<11?m three grained levels?were determined by Sr-Nd isotopes.The main results are as follows:?1?of different particle size components,there are obvious differences in heavy mineral content,heavy mineral index?ATi,GZi and ZTR?and heavy mineral assemblages,which are shown as garnet,monazite,sphene enriched in coarser particles;hematite,anatase,ilmenite,rutile,tourmaline,and zircon enriched in finer particles.The average Ati index of the two components was not significantly different,the GZi index of the?73-125?m?component was larger than that of the?<73?m?component,and the ZTR index of the?<73?m?component was higher than that of the?73-125?m?component.there are differences in the ATi and ZTR indices under the GZi index,which have little effect on the GZi index.In the separation process,the stability and extreme stability of minerals are preferentially enriched in fine particles,thereby enhancing the overall stability of fine-grained sediments.?2?Under the same source conditions,the composition characteristics of heavy minerals of different samples of the same size fraction are significantly different,and the particle size effect is obvious.Therefore,in the use of heavy minerals for provenance tracing research,multi-indicator comprehensive analysis is needed,and it is difficult for a single sample to have regional representativeness.It is necessary to ensure a sufficient sample volume and compare them in the same size.?3?The 87Sr/86Sr ratio of Hulunbeir sandy land is significantly lower than that of Loess Plateau and slightly lower than that of Northern Boundary Desert,but the value of?Nd?0?is slightly lower than that of Northern Boundary Desert and slightly higher than Loess Plateau.The 87Sr/86Sr ratio is little affected by particle size,but the Nd isotopic composition is influenced by particle size effect and shows coarse particle composition trend of higher Nd isotope ratios.The time effect of Sr-Nd isotopic composition,which changes with time,indicates the instability of geochemical composition in the dust source area,which is important for understanding the source change of sediment.?4?The geochemical and Sr-Nd isotopic composition of the Hulunbeier sandy land and the Harbin loess and dust storm sediments are quite different,which indicates that the Hulunbeier sandy land cannot be a potential source area of Harbin loess. |
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